1. Field of the Invention
The present invention relates to an ink composition for a writing tool and to a writing tool.
2. Related Background Art
A variety of colors are realized in ink compositions for writing tools, by the use of various dyes and pigments. Ink compositions with metallic colors obtained by including metal powders, and writing tools comprising such ink compositions, have been proposed in recent years in Japanese Patent Publication No. 3221846 (hereinafter referred to as “document 1”) and Japanese Patent Publication No. 3789198 (hereinafter referred to as “document 2”).
Because ink compositions containing such metal powders contain solid metal powder, problems have been faced including writing problems such as ink bleed-out and writing thin spots, settling of the metal powder during storage or use causing separation of the ink composition, clogging of the pen point or alteration in color tone with passage of time.
In order to avoid these problems, certain proposals have involved specifying the clearance size between the ball and ball-holding chamber in the ball-point pen tip structure (document 1), or including an alkali of an unsaturated fatty acid as a specific component (document 2).